Dithiol compounds, derivatives, and uses therefor

ABSTRACT

Dithiol compounds and derivatives thereof are disclosed. The agents are useful for treating ocular disease, especially presbyopia and cataract.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 14/303,405, filed Jun. 12, 2014, now U.S. Pat. No.9,284,305, which is a divisional application of U.S. patent applicationSer. No. 12/815,586, filed Jun. 15, 2010, now U.S. Pat. No. 8,795,706,which claims the benefit of U.S. Provisional Application Nos.61/187,005; 61/187,018; 61/187,023; 61/186,986; 61/187,028; 61/187,033;61/187,039; 61/186,940; each of which was filed on Jun. 15, 2009, andU.S. Provisional Application Nos. 61/224,930, filed Jul. 13, 2009;61/235,051, filed Aug. 19, 2009; 61/237,912, filed Aug. 28, 2009; and61/242,232, filed Sep. 14, 2009.

Each of these applications is incorporated herein by reference in itsentirety and for all purposes.

BACKGROUND OF THE INVENTION

As we age, our lenses undergo physiological changes that make it moredifficult to focus on near objects. That is why nearly everyone requiresreading glasses, even as early as age 35-40. The ability of the eye tochange focal power, also known as accommodative amplitude, decreasessignificantly with age. The accommodative amplitude is 20 diopters inchildren and young adults, but it decreases to 10 diopters by age 25 andto ≦1 diopter by age 60. The age-related inability to focus on nearobjects is called presbyopia. All of us will develop presbyopia and willrequire corrective lenses unless a new treatment is found.

Both presbyopia and cataract are age-related and may share commonetiologies such as lens growth, oxidative stress, and/or disulfide bondformation.

There is a need for agents, compositions, and methods for combatingocular disease, including presbyopia and/or cataract.

BRIEF SUMMARY OF THE INVENTION

In one aspect, a compound is provided having the structure of Formula Ior pharmaceutically acceptable salt thereof:

In Formula I and I-NC, each of X and Y can be sulfur, selenium, or asulfonic group. In one embodiment, X and Y are both sulfur. In anotherembodiment, one of X and Y is sulfur, and the other is sulfur orselenium. R₁₉ is substituted or unsubstituted alkylene. Each of R₂₀, R₂₁R₃₀, and R₃₁ is independently hydrogen, substituted or unsubstitutedalkyl, substituted or unsubstituted cycloalkyl, substituted orunsubstituted heteroalkyl, substituted or unsubstitutedheterocycloalkyl, substituted or unsubstituted aryl, or substituted orunsubstituted heteroaryl. Z is N or O. Variable m is 0 or 1, wherein ifZ is N, then m is 1, and if Z is O, then m is 0. In one embodiment, R₃₀and R₃₁ together form a single bond (thereby creating a structure ofFormula I) or are they are substituents joined together to form aheteroocyclic ring including X and Y.

In another embodiment, a compound of Formula I, or a pharmaceuticallyacceptable salt thereof, is employed for pharmaceutical formulations(including a pharmaceutically acceptable excipient) and/or methods oftreating ocular disease, e.g., presbyopia or cataract.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the accommodative amplitude in diopters (D) of anuntreated human lens as a function of age in years. Borja, D et al.2008. Optical Power of the Isolated Human Crystalline Lens. InvestOphthalmol Vis Sci 49(6):2541-8. Borja et al. calculated the maximumpossible accommodative amplitude of each measured lens power data point(n=65). As shown, there is good agreement between the age-dependent lossof accommodation and the maximum amplitude of accommodation calculatedfrom the isolated lens power.

FIG. 2 shows a trend graph of the shear modulus versus position in thelens and age. Weeber, H A et al. 2007. Stiffness gradient in thecrystalline lens. Graefes Arch Clin Exp Ophthalmol 245(9):1357-66. Theline at the bottom is the 20-year-old lens; the line at the top is the70-year-old lens. The modulus increases with age for all positions inthe lens. Measurements were taken up to 4.0 mm from the lens centre. Thelines are extrapolated to a radius of 4.5 mm (lens diameter 9.0 mm).

FIG. 3 depicts the average opacity (opacimetry) of an untreated humanlens as a function of age in years. Bonomi, L et al. 1990. Evaluation ofthe 701 interzeag lens opacity meter. Graefe's Arch Clin Exp Ophthalmol228(5):447-9. Lens opacity was measured in 73 healthy subjects between10 and 76 years of age without slit-lamp evidence of cataract and with avisual acuity of 20/20. These subjects were classified into ten agegroups. This study was carried out using the Interzeag Opacity Meteraccording to the procedure described by Flammer and Bebies (Flammer J,Bebie H. 1987. Lens Opacity Meter: a new instrument to quantify lensopacity. Ophthalmologica 195(2):69-72) and following the suggestions ofthe operating manual for the instrument.

FIG. 4 depicts a scatter plot of the change in ΔD (micrometers) in theabsence (control) and presence of lipoic acid in lens organ cultureexperiments. The symbol ‡ designates significantly larger changes in ΔDwhen compared to controls. Statistical values are highly significant atp<0.0001 by unpaired t-test and by Kruskal Wallis test, which comparedmedians of each data set. The relative change in Young's modulus (E) canbe calculated as the cubic value derived from the ΔD of the controldivided by the ΔD of the experimental or E fractional change=(ΔDcon/ΔDexp)^3.

FIG. 5 depicts a scattergram of the percent of the total protein SHgroups in disulfide bonds. Free SH groups were alkylated with4-acetamido-4′-maleimidylstilbene-2,2′-sulfonic acid (c, 1 μM, 5 μM, 9.6μM, 50 μM, 96 μM) or 7-diethylamino-3-(4′maleimidylphenyl)-4-methylcoumarin (500 μM, and 500 μM c). Following removal of the firstalkylating agent, the S—S bonds were reduced and alkylated withfluorescein-5-maleimide. Absorption spectra were used to calculatedtotal protein (A280 nm), free protein SH (A322 or A384), and protein SS(A490) using the appropriate extinction coefficients. The symbol ‡indicates statistically significant difference of mean with mean ofcontrol (c, p≦0.05). The symbol ** indicates means of 500 μM lipoic acidand the 500 μM control were significantly different from each other(p=0.027).

DETAILED DESCRIPTION OF THE INVENTION

I. Definitions

The abbreviations used herein have their conventional meaning within thechemical and biological arts. The chemical structures and formulae setforth herein are constructed according to the standard rules of chemicalvalency known in the chemical arts.

Where substituent groups are specified by their conventional chemicalformulae, written from left to right, they equally encompass thechemically identical substituents that would result from writing thestructure from right to left, e.g., —CH₂O— is equivalent to —OCH₂—. Inother words, no orientation is implied by the direction that the groupis written.

The term “alkyl,” by itself or as part of another substituent, means,unless otherwise stated, a straight (i.e., unbranched) or branchedchain, or combination thereof, which may be fully saturated, mono- orpolyunsaturated (i.e., alkenyl) and can include di- and multivalentradicals (e.g., alkylene), having the number of carbon atoms designated(i.e., C₁-C₁₀ means one to ten carbons). Examples of saturatedhydrocarbon radicals include, but are not limited to, groups such asmethyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, isobutyl,sec-butyl, (cyclohexyl)methyl, homologs and isomers of, for example,n-pentyl, n-hexyl, n-heptyl, n-octyl, and the like. An unsaturated alkylgroup is one having one or more double bonds or triple bonds. Examplesof unsaturated alkyl groups (i.e., alkenyl groups) include, but are notlimited to, vinyl, 2-propenyl, 2-isopentenyl, 2-(butadienyl),2,4-pentadienyl, 3-(1,4-pentadienyl), ethynyl, 1- and 3-propynyl,3-butynyl, and the higher homologs and isomers. An alkoxy is an alkylattached to the remainder of the molecule via an oxygen linker (—O—). Analkthio is an alkyl attached to the remainder of the molecule via asulfur linker (—S—).

The term “heteroalkyl,” by itself or in combination with another term,means, unless otherwise stated, a stable straight or branched chain, orcombinations thereof, consisting of at least one carbon atom and atleast one heteroatom. A “heteroatom” includes oxygen (O), nitrogen (N),sulfur (S), phosphorus (P), selenium (Se) and silicon (Si), wherein Nand S may optionally be oxidized, and N may optionally be quaternized. Aheteroatom(s) may be placed at any chemically acceptable positionincluding an interior position, the position at which the alkyl group isattached to the remainder of the molecule (the proximal end), or at thedistal end (e.g., for heteroalkylene groups). Examples include, but arenot limited to: —C(O)R′, —C(O)NR′, —NR′R″, —OR′, —SR′, and/or —SO₂R′,and —CN. Up to two heteroatoms may be consecutive, such as, for example,—CH₂—NH—OCH₃.

The terms “cycloalkyl” and “heterocycloalkyl,” by themselves or incombination with other terms, mean, unless otherwise stated, cyclicversions of “alkyl” and “heteroalkyl,” respectively. Examples ofcycloalkyl include, but are not limited to, cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, and cycloheptyl. Examples of heterocycloalkylinclude, but are not limited to, piperidinyl, piperazinyl, morpholinyl,tetrahydrofuranyl, and tetrahydrothienyl.

The term “aryl” by itself or in combination with another term, means,unless otherwise stated, a polyunsaturated, aromatic, hydrocarbon group,which can be a single ring or multiple rings (preferably from 1 to 3rings) that are fused together or linked covalently. A fused ring arylrefers to multiple rings fused together wherein at least one of thefused rings is an aryl ring.

The term “heteroaryl” by itself or in combination with another term,means, unless otherwise stated an aryl group (as defined above)containing one to four heteroatoms (as defined above). Thus, the term“heteroaryl” includes fused ring heteroaryl groups, which are multiplerings (e.g., 5 and/or 6-membered rings) fused together wherein at leastone of the fused rings is a heteroaromatic ring. A heteroaryl group canbe attached to the remainder of the molecule through a carbon orheteroatom. Non-limiting examples of aryl and heteroaryl groups includephenyl, naphthyl, pyrrolyl, pyrazolyl, imidazolyl, pyrazinyl, oxazolyl,thiazolyl, furyl, thienyl, pyridyl, pyrimidyl, purinyl, benzothiazolyl,benzimidazolyl, indolyl, isoquinolyl, quinoxalinyl, 5-quinoxalinyl, andquinolyl.

For brevity, the term “aryl” when used in combination with other terms(e.g., aryloxy, arylthioxy, arylalkyl) includes both aryl and heteroarylrings as defined above. Thus, the term “arylalkyl” is meant to includethose radicals in which an aryl group is attached to an alkyl group(e.g., benzyl, phenethyl, pyridylmethyl, and the like) including thosealkyl groups in which a carbon atom (e.g., a methylene group) has beenreplaced by, for example, an oxygen atom (e.g., phenoxymethyl,2-pyridyloxymethyl, 3-(1-naphthyloxy)propyl, and the like).

For any of the above groups-alkyl, heteroalkyl, cycloalkyl,heterocycloalkyl, aryl, and heteroaryl—the corresponding divalentradical may be referred to with the suffix -ene.

Regarding size, the non-cyclical groups (alkyl and heteroalkyl)typically have 1 to 24 atoms, preferably 1 to 10 atoms, more preferably1 to 8 atoms (referred to as “lower” substituent group). The cyclicalgroups (cycloalkyl, heterocycloalkyl, aryl, and heteroaryl) typicallyhave from 3 to 8 members, preferably 4 to 8 members, more preferably 5to 7 members.

Any of the above groups-alkyl, heteroalkyl, cycloalkyl,heterocycloalkyl, aryl, and heteroaryl—may be unsubstituted orsubstituted. Exemplary substituents are described below. Further, thesubstituents themselves may also be unsubstituted or substituted.

A “substituent group,” as used herein, means a group selected from thefollowing moieties:

-   -   (A) —OH, —NH₂, —SH, —CN, —CF₃, —NO₂, oxo, halogen, unsubstituted        alkyl, unsubstituted heteroalkyl, unsubstituted cycloalkyl,        unsubstituted heterocycloalkyl, unsubstituted aryl,        unsubstituted heteroaryl, and    -   (B) alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, and        heteroaryl, substituted with at least one substituent selected        from:        -   (i) oxo, —OH, —NH₂, —SH, —CN, —CF₃, —NO₂, halogen,            unsubstituted alkyl, unsubstituted heteroalkyl,            unsubstituted cycloalkyl, unsubstituted heterocycloalkyl,            unsubstituted aryl, unsubstituted heteroaryl, and        -   (ii) alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl,            and heteroaryl, substituted with at least one substituent            selected from:            -   (a) oxo, —OH, —NH₂, —SH, —CN, —CF₃, —NO₂, halogen,                unsubstituted alkyl, unsubstituted heteroalkyl,                unsubstituted cycloalkyl, unsubstituted                heterocycloalkyl, unsubstituted aryl, unsubstituted                heteroaryl, and            -   (b) alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl,                aryl, or heteroaryl, substituted with at least one                substituent selected from: oxo, —OH, —NH₂, —SH, —CN,                —CF₃, —NO₂, halogen, unsubstituted alkyl, unsubstituted                heteroalkyl, unsubstituted cycloalkyl, unsubstituted                heterocycloalkyl, unsubstituted aryl, and unsubstituted                heteroaryl.

The terms “halo” or “halogen” by themselves or as part of anothersubstituent, mean, unless otherwise stated, a fluorine, chlorine,bromine, or iodine atom. Additionally, terms such as “haloalkyl” aremeant to include monohaloalkyl and polyhaloalkyl. For example, the term“halo(C₁-C₄)alkyl” includes, but is not limited to, fluoromethyl,difluoromethyl, trifluoromethyl, 2,2,2-trifluoroethyl, 4-chlorobutyl,3-bromopropyl, and the like.

The term “acyl” means —C(O)R where R is a substituted or unsubstitutedalkyl, substituted or unsubstituted cycloalkyl, substituted orunsubstituted heteroalkyl, substituted or unsubstitutedheterocycloalkyl, substituted or unsubstituted aryl, or substituted orunsubstituted heteroaryl.

The term “oxo,” as used herein, means an oxygen that is double bonded toa carbon atom.

The term “alkylsulfonyl” means a moiety having the formula —S(O₂)—R′,where R′ is an alkyl group as defined above. R′ may have a specifiednumber of carbons (e.g., “C₁-C₄ alkylsulfonyl”).

The substituents can be one ore more one or more of a variety of groupsselected from, but not limited to, —OR′, —NR′R″, —SR′, -halogen,—SiR′R″R′″, —OC(O)R′, —C(O)R′, —CO₂R′, —CONR′R″, —OC(O)NR′R″,—NR″C(O)R′, —NR′—C(O)NR″R′″, —NR″C(O)₂R′, —NR—C(NR′R″R′″)═NR′″,—NR—C(NR′R″)═NR′″, —S(O)R′, —S(O)₂R′, —S(O)₂NR′R″, —NRSO₂R′, —CN, and—NO₂. Substituents for the non-aromatic groups (alkyl, heteroalkyl,cycloalkyl, and heterocycloalkyl) may also include, e.g., ═O, ═NR′, and═N—OR′. Each of R′, R″, R′″, and R″″ can be independently hydrogen,substituted or unsubstituted alkyl, substituted or unsubstitutedcycloalkyl, substituted or unsubstituted heteroalkyl, substituted orunsubstituted heterocycloalkyl, substituted or unsubstituted aryl, orsubstituted or unsubstituted heteroaryl. From the above discussion ofsubstituents, one of skill in the art will understand that the term“alkyl” is meant to include groups including carbon atoms bound togroups other than hydrogen groups, such as haloalkyl (e.g., —CF₃ and—CH₂CF₃) and acyl (e.g., —C(O)CH₃, —C(O)CF₃, —C(O)CH₂OCH₃).

Substituents for the non-aromatic groups may be present in any numberfrom zero to (2m′+1), where m′ is the total number of carbon atoms inthe group. Substituents for the aromatic groups (aryl and heteroaryl)may be present in any number from zero to the total number of openvalences on the aromatic ring system.

Two or more substituents may optionally be joined to form aryl,heteroaryl, cycloalkyl, or heterocycloalkyl groups. Such so-calledring-forming substituents are typically, though not necessarily, foundattached to a cyclic base structure. In one embodiment, the ring-formingsubstituents are attached to adjacent members of the base structure. Forexample, two ring-forming substituents attached to adjacent members of acyclic base structure create a fused ring structure. In anotherembodiment, the ring-forming substituents are attached to a singlemember of the base structure. For example, two ring-forming substituentsattached to a single member of a cyclic base structure create aspirocyclic structure. In yet another embodiment, the ring-formingsubstituents are attached to non-adjacent members of the base structure.

The symbol

denotes the point of attachment of a chemical moiety to the remainder ofa molecule or chemical formula.

Certain compounds of the present invention possess asymmetric carbonatoms (optical centers) or double bonds; the racemates, diastereomers,tautomers, geometric isomers, and individual isomers are encompassedwithin the scope of the present invention. The compounds of the presentinvention do not include those that are known in the art to be toounstable to synthesize and/or isolate.

The compounds of the present invention may also contain unnaturalproportions of atomic isotopes at one or more of the atoms thatconstitute such compounds. For example, the compounds may beradio-labeled with radioactive isotopes, such as for example tritium(³H), iodine-125 (¹²⁵I), or carbon-14 (¹⁴C). All isotopic variations ofthe compounds of the present invention, whether radioactive or not, areencompassed within the scope of the present invention.

Any numerical values recited herein include all values from the lowervalue to the upper value in increments of any measurable degree ofprecision. For example, if the value of a variable such as age, amount,time, percent increase/decrease and the like is 1 to 90, specificallyfrom 20 to 80, and more specifically from 30 to 70, it is intended thatvalues such as 15 to 85, 22 to 68, 43 to 51, 30.3 to 32, etc., areexpressly enumerated in this specification. In other words, all possiblecombinations of numerical values between the lowest value and thehighest value enumerated are to be considered to be expressly stated inthis application in a similar manner.

II. Compounds

There are provided agents, compositions, and methods that can prevent,reduce, reverse, and/or slow the rate of lens growth, oxidative damage,and/or disulfide bond formation. In some embodiments, these agents,compositions, and methods can effectively prevent or treat presbyopiaand/or cataract. In one embodiment, the agents, compositions, andmethods can effectively prevent or treat presbyopia.

A. Dithiol Compounds and Derivatives

In some embodiments, the agents described herein are dithiol compoundsor dithiol derivatives. Dithiol compounds contain at least two sulfuratoms, preferably exactly two sulfur atoms, while dithiol derivativesinclude a selenium or sulfonic group in place of one or more sulfuratoms of a dithiol compound. Thus, in one embodiment, the agent has atleast two components, each independently selected from a sulfur atom, aselenium atom, and a sulfonic group. In another embodiment, the agenthas at least two components, each independently selected from a sulfuratom and a selenium atom.

In some embodiments, the agents contemplated herein can be cyclical,e.g., a five- or six-membered heterocycle, or non-cyclical. Exemplaryfive-membered heterocycles (designated by the term “Formula 5” in thecompound name) include, but are not limited to:

Exemplary six-membered heterocycles (designated by the term “Formula 6”in the compound name) include, but are not limited to:

Exemplary non-cyclical agents (designated by the term “NC” affixed tothe formulae designations) include, but are not limited to:

The agents can be classified in various ways. For example, the agent canbe encompassed by any one of the following classification groups:

-   -   5A, 5B, 6A, 6B, 6C, 6D, and 6E: “cyclical”    -   5-NC, 6-NC, and NC: “non-cyclical”    -   5A, 5B, and 5-NC: “5-membered”    -   5A and 5B: “5-membered cyclical”    -   6A, 6B, 6C, 6D, 6E, and 6-NC: “6-membered”    -   6A, 6B, 6C, 6D, and 6E: “6-membered cyclical”    -   5A and 5-NC: “potential hydrogenation pair”    -   6A and 6-NC: “potential hydrogenation pair”    -   5-NC and 6-NC: “potential hydrogenation products”    -   5A, 6A, 6D, and 6E: “adjacent thiols”    -   5A and 6A: “adjacent thiols, saturated ring”    -   6A, 6D, and 6E: “adjacent thiols, 6-membered cyclical”    -   5B, 6B, and 6C: “non-adjacent thiols”    -   5B and 6B: “1,3 thiols”    -   6A, 6B, and 6C: “dithanes”    -   6D and 6E: “dithiines”    -   or the agents can be classified by any individual formula.

In some embodiments, substituents X and Y of any of Formulae 5A-B, 6A-Eor NC are independently selected from a sulfur atom, a selenium atom,and a sulfonic group. Preferably, at least one of X and Y is sulfur. Inone embodiment, X and Y are both sulfur. In another embodiment, one of Xand Y is sulfur, and the other is sulfur or selenium. In yet anotherembodiment, one of X and Y is sulfur, and the other is selenium. In oneembodiment, the compound of any of Formulae 5A-B, 6A-E or NC is a selenoderivative where at least one of X and Y is selenium. Without beingbound by theory, it is believed that the selenium atom advantageouslyhelps to overcome redox potential.

In some embodiments, each R group of Formulae 5A-B, 6A-E or NC isindependently —H, —OH, —OAc, —OR, —SR′, —CO₂R′, an electron withdrawinggroup, a linear or branched C₁₋₁₈ alkyl optionally substituted by one ormore ether, ester, carboxylic acid, phosphate, amide, and/or aminegroups, wherein R′ is hydrogen, substituted or unsubstituted alkyl,substituted or unsubstituted heteroalkyl, substituted or unsubstitutedcycloalkyl, substituted or unsubstituted heterocycloalkyl, substitutedor unsubstituted aryl, or substituted or unsubstituted heteroaryl. Insome embodiments, each R group is independently —H, —OH, —OAc, —CO₂CH₃,or a linear C₁₋₁₈ alkyl optionally having a distal terminal that is—COOH, —NH₂, —CO₂CH₃, or —CO₂CH₂CH₃. It is understood that, absentfurther description, the term “R group” in the context of compounds ofany of the formulae described herein refers to any of R₁, R₂, R₃, R₄,R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, R₁₅, R₁₆, R₁₇ or R₁₈, R₁₉,R₂₀, R₂₁, R₂₂, R₂₃, R₂₄, R₂₅, R₂₆, R₂₇, R₂₈, R₂₉, R₃₀, R₃₁, R₃₂, R₃₃,and/or R₃₄.

In some embodiments, agents can be prepared by altering the placement ofa particular R group. For example, any particular R group can beattached to a carbon adjacent to a thiol group (sulfur atom) or thiolderivative (e.g., selenium or sulfonic group). R₁, R₂, R₇, R₈, R₉, R₁₀,R₁₁, R₁₂, R₁₃, and R₁₄ represent such thiol-adjacent positions. In otherembodiments, an R group can be attached to a carbon not adjacent to athiol group or thiol derivative. R₃, R₄, R₅, and R₆ represent suchnon-adjacent positions. In yet other embodiments, an R group can beattached directly to a thiol group or thiol derivative. R₁₅, R₁₆, R₁₇,and R₁₈ represent such direct thiol or thiol derivative attachments.

In one embodiment, one, two, or more R groups are —H. In someembodiments of Formula 5-NC and 6-NC, both of R₁₅ and R₁₆ are —H.

In one embodiment, one, two, or more R groups are —OH.

In another embodiment, one, two, or more R groups are —OAc. Withoutbeing bound by theory, the addition of an acetate ester (—OAc) isbelieved to improve corneal permeability, which is especially beneficialfor the treatment of presbyopia.

In yet another embodiment, each R group is independently —H, —OH, —OAc,or —CH₃. In another embodiment, one R group is a chain substituent(e.g., substituted or unsubstituted alkyl, preferably a C₁₋₁₈ alkyl),and the remaining R groups are independently —H, —OH, —OAc, or —CH₃.

In one embodiment, the agent has the structure of Formula 6A:

wherein each of R₁, R₂, R₇, and R₈ is —H; and R₃, R₄, R₅, and R₆ areindependently selected from —H, —OH, and —OAc.

In another embodiment, one, two, or more R groups are —CO₂R′, wherein R′is as defined herein for any of Formulae 5A-B, 6A-E or NC. In anotherembodiment, one, two, or more R groups are —OR′. In some embodiments,the R′ of —CO₂R′ or —OR′ is a lower alkyl group having 1-8 carbons. Inone embodiment, —CO₂R′ is —CO₂CH₃.

In some embodiments, the agent can be modified by altering the length ofthe chain substituent(s). Without being bound by theory, longer chainsare believed to render the compound more hydrophobic, more lipidsoluble, and thus more easily transported across the cell membrane. Thelength of the chain is limited by the lipid membrane width; a chainlonger than the membrane width is likely to cause saponification.Shorter chains, on the other hand, and other similarly smallsubstituents such as —OH and —CO₂CH₃, may be useful for preparing agentsthat are biologically active in the cytosol and do not require membranepermeability. Substituent size and its concomitant effect on solubilityalso affect formulation considerations. For example, a hydrophobic drugmay be more difficult to formulate as an administratable solution, butit may be more easily formulated for sustained release delivery systems.

In one embodiment, the agent includes a linear substituted orunsubstituted C₁₋₁₈ alkyl or heteroalkyl, which are collectivelyreferred to herein as “linear substituents.” The term “branchedsubstituent” refers to substituted or unsubstituted branched C₁₋₁₈ alkylor heteroalkyl.

Without being bound by theory, linear substituents are more commonlyfound in natural compounds, so agents including linear substituents maybe better tolerated by the body.

However, branched substituents may also be used. The linear substituentcan be, for example, attached to a carbon adjacent to a thiol group(sulfur atom) or thiol derivative (e.g., selenium or sulfonic group). Insome embodiments, one or more of R₁, R₂, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃,and R₁₄ is a linear substituent. In other embodiments, one or more ofR₃, R₄, R₅, and R₆ is a linear substituent.

In one embodiment, a chain substituent (e.g., substituted orunsubstituted alkyl, preferably a C₁₋₁₈ alkyl) includes an ether, ester,carboxylic acid, phosphate, amide, and/or amine group at the distalterminal of a chain. In one embodiment, the distal terminal is acarboxylic acid or an amine. In another embodiment, one, two, or more Rgroups are —(CH₂)₂₋₁₀CO₂H or —(CH₂)₂₋₁₀NH₂. Without being bound bytheory, it is believed that carboxylic acid and amine terminals provideattachment points for natural amino acids to form peptide amide bonds.For example, the carboxylic acid terminal of exemplary agent lipoic acidis often covalently attached to the amine lysine side chain of theactive mitochondrial enzyme. The mitochondrial functionality of lipoicacid is discussed in further detail below.

In another embodiment, the distal terminal of a chain substituent is anester, e.g., methyl, ethyl, or isopropyl ester. In one embodiment, one,two, or more R groups are —(CH₂)₂₋₁₀CO₂CH₃ or —(CH₂)₂₋₁₀CO₂CH₂CH₃.Without being bound by theory, esterification is believed to be one wayto modify the delivery of the pharmaceutical agent since the agent isinhibited from entering the cell until the ester is broken, e.g., bynaturally occurring esterases. In this way, an esterified agent canserve as a prodrug that can be converted to an active form, as known inthe art.

In one embodiment, the linear substituent is a substituted orunsubstituted linear C₁₋₁₈, C₂₋₁₂, C₂₋₁₀, C₂₋₈, C₂₋₆, C₄₋₆, C₅₋₆, or C₅alkyl. Exemplary agents including a linear alkyl substituent areprovided in Table 1 following, wherein the remaining R groups which arenot expressly defined in Table 1 are independently —H, —OH, —OAc, or—CH₃.

TABLE 1 Formula X, Y R 5A; X is S and Y is S R₁ or R₃ is: 5-NC; or—(CH₂)₃₋₁₀CO₂H; 6B —(CH₂)₃₋₁₀CO₂CH₃; or —(CH₂)₃₋₁₀CO₂CH₂CH₃ 5A; X is Sand Y is S; R₁ or R₃ is: 5-NC; or X is S and Y is Se; or —(CH₂)₁₋₂CO₂H;6B X is Se and Y is S —(CH₂)₁₋₂CO₂CH₃; —(CH₂)₁₋₂CO₂CH₂CH₃; or—(CH₂)₂₋₁₀NH₂ 5A X is S and Y is Se; or R₁ or R₃ is: 5-NC X is Se and Yis S —(CH₂)₃₋₁₀CO₂H; 6B —(CH₂)₃₋₁₀CO₂CH₃; or —(CH₂)₃₋₁₀CO₂CH₂CH₃ 6A X isS and Y is S; R₁ or R₃ is: 6-NC X is S and Y is Se; or —(CH₂)₂₋₁₀CO₂H; Xis Se and Y is S —(CH₂)₂₋₁₀NH₂; —(CH₂)₂₋₁₀CO₂CH₃; or —(CH₂)₂₋₁₀CO₂CH₂CH₃5B X is S and Y is S; R₁ or R₉ is: X is S and Y is Se; or—(CH₂)₂₋₁₀CO₂H; X is Se and Y is S —(CH₂)₂₋₁₀NH₂; —(CH₂)₂₋₁₀CO₂CH₃; or—(CH₂)₂₋₁₀CO₂CH₂CH₃ 6D X is S and Y is S; R₁, R₃, R₅, or R₇ is: 6E X isS and Y is Se; or —(CH₂)₂₋₁₀CO₂H; X is Se and Y is S —(CH₂)₂₋₁₀NH₂;—(CH₂)₂₋₁₀CO₂CH₃; or —(CH₂)₂₋₁₀CO₂CH₂CH₃

Exemplary agent lipoic acid and some derivatives thereof include adivalent linear alkylene functionality with a carboxylic acid terminal:

In one embodiment, the agent is lipoic acid(5-(1,2-dithiolan-3-yl)pentanoic acid), particularly alpha lipoic acid.In another embodiment, the agent is a lipoic acid derivative. Preferredlipoic acid derivatives do not interfere with the natural cellularmechanisms utilizing lipoic acid and/or dihydrolipoic acid. The agentsdescribed herein include those having relatively minor modifications tolipoic acid (e.g., altering chain length, replacing a sulfur atom withselenium) such that naturally occurring mitochondrial mechanisms canutilize either lipoic acid or the derivative. Agents having minormodifications may be relatively substitutable for lipoic acid and do notinterfere with mitochondrial activity. Thus, in one embodiment, theagent functionally mimics lipoic acid in terms of redox activity and/ormitochondrial activity, but is not structurally identical to lipoicacid. Other agents include those having more major modifications tolipoic acid (e.g., altering chain placement). Such major modificationsmay render the agent unrecognizable to the mitochondria, thus avoidinginterference with cellular mechanisms. In this way, both minor and majormodifications can avoid mitochondrial interference. Mitochondrialinterference, or the lack thereof, can be verified by in vitro testingaccording to methods known in the art such as, for example, a JC-1Mitochondrial Membrane Potential Assay Kit (Cell Tech. Inc.). One ofordinary skill in the art could balance the strength of the reducingagent, which is believed to be responsible for the therapeutic effect,against mitochondrial interference, which might cause adverse effects.Exemplary lipoic acid derivatives include, but are not limited to:5-(1,2-thiaselenolan-5-yl)pentanoic acid and5-(1,2-thiaselenolan-3-yl)pentanoic acid.

Without being bound by theory, it is believed that lipoic acid orderivatives thereof, may upregulate antioxidant pathways (e.g.,thioredoxin). Key to this upregulation is the Nrf2 response element. SeeLi, X., Liu, Z., et al. 2008. Lipoamide protects retinal pigmentepithelial cells from oxidative stress and mitochondrial dysfunction.Free Radic Biol Med. 44(7): 1465-1474. This suggests that the mechanismof action for lipoic acid and derivatives includes not only itsantioxidant properties, but also an upregulation of other enzymes.

In another embodiment, the linear substituent is a linear C₁₋₁₈, C₁₋₈,C₅₋₁₅, C₁₀₋₁₈, or C₁₀₋₁₆, or C₁₂₋₁₄ alkenyl, the alkenyl chain of whichcan have one, two, three, or more double bonds. Without being bound bytheory, linear alkenyls of relatively longer length, e.g., C₁₀₋₁₈,particularly those including a carboxylic acid or ester group, mayexhibit advantageous properties similar to a fatty acid group.

Alkenyls, including those of shorter lengths, are also useful,especially for embodiments of Formula NC. For example, in oneembodiment, each of R₁₇ and R₁₈ is independently selected from C₂₋₈,C₂₋₆, C₃₋₆, C₃₋₅, or C₃ alkenyl. In another embodiment of Formula NC,R₁₇ and/or R₁₈ is an —SC₂₋₈ alkenyl.

A chain substituent can include more than one substituent. For example,one exemplary agent is cystine (3,3′-disulanedylbis(2-aminopropanoicacid)), which includes both carboxylic acid and amine substituents. Inone embodiment, the agent is cystine or a derivative thereof such as theexemplary derivative shown below:

In another embodiment, an R group substituent is an electron withdrawinggroup, which can decrease the pKa of the agent. Electron withdrawinggroups include, but are not limited to halogens (e.g., F, Cl), nitriles(CN), carboxylic acids (COOH), and carbonyls (CO).

In one embodiment, the agent is an allium oil antioxidant or aderivative thereof. Allium oil antioxidants are advantageously natural,nontoxic, and lipid soluble. Some have been studied as potentialcytostatic agents for the treatment of atherlerosclerosis, cancer, etc.Without being bound be theory, the cytostatic properties may alsoprovide advantageous efficacy in the context of ocular diseases causedby lens growth, including presbyopia and cataract.

One class of allium oil antioxidants is the dithiines. Exemplarydithiines include, but are not limited to:

Other allium oil antioxidants include, but are not limited to:

In another embodiment, the agent can be a dithiane or a derivativethereof. Without being bound by theory, it is believed that dithianesincrease cellular non-protein SH, a primary objective in the treatmentof presbyopia. Exemplary dithianes include, but are not limited to:

In one embodiment, the agent is a derivative of dithiothreitol (DTT)such as trans-4,5-dihydroxy-1,2-dithiane, also referred to herein as“non-lethal DTT”:

Both DTT and non-lethal DTT possess potent antioxidant properties, butnon-lethal DTT possesses the further advantage of reduced toxicitythereby being more favorable for use in in vivo settings.

B. Amides and Esters

In certain embodiments, the compound is a heterocyclic ester or amidehaving the structure of Formula I:

wherein X and Y are as defined above, and Z is nitrogen (N) or oxygen(O), and m is 0 or 1, wherein if Z is N, then m is 1, and if Z is O,then m is 0.

R₁₉ is R₂₂-substituted or unsubstituted alkylene, or R₂₂-substituted orunsubstituted heteroalkylene, wherein R₂₂ is independently substitutedor unsubstituted alkyl, substituted or unsubstituted cycloalkyl,substituted or unsubstituted heteroalkyl, substituted or unsubstitutedheterocycloalkyl, substituted or unsubstituted aryl, or substituted orunsubstituted heteroaryl. In one embodiment, R₁₉ is a substituted orunsubstituted alkylene, e.g., a C₁₋₈, C₁₋₆, C₃₋₅, or C₄ alkylene.

R₂₀ is hydrogen, R₂₃-substituted or unsubstituted alkyl, R₂₃-substitutedor unsubstituted cycloalkyl, R₂₃-substituted or unsubstitutedheteroalkyl, R₂₃-substituted or unsubstituted heterocycloalkyl,R₂₃-substituted or unsubstituted aryl, or R₂₃-substituted orunsubstituted heteroaryl. R₂₃ is independently —NH₂, ═NH, —PO₃H₂, —OH,—CO₂H, R₂₄-substituted or unsubstituted alkyl, R₂₄-substituted orunsubstituted cycloalkyl, R₂₄-substituted or unsubstituted heteroalkyl,R₂₄-substituted or unsubstituted heterocycloalkyl, R₂₄-substituted orunsubstituted aryl, or R₂₄-substituted or unsubstituted heteroaryl. R₂₄is independently —NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₂₅-substituted orunsubstituted alkyl, R₂₅-substituted or unsubstituted cycloalkyl,R₂₅-substituted or unsubstituted heteroalkyl, R₂₅-substituted orunsubstituted heterocycloalkyl, R₂₅-substituted or unsubstituted aryl,or R₂₅-substituted or unsubstituted heteroaryl. R₂₅ is independentlyunsubstituted alkyl, unsubstituted cycloalkyl, unsubstitutedheteroalkyl, unsubstituted heterocycloalkyl, unsubstituted aryl orunsubstituted heteroaryl. In some embodiments, R₂₀ is hydrogen or anunsubstituted lower alkyl, e.g., methyl, ethyl, propyl, or butyl. Inanother embodiment, R₂₀ is hydrogen.

R₂₁ is R₂₆-substituted or unsubstituted alkyl, R₂₆-substituted orunsubstituted cycloalkyl, R₂₆-substituted or unsubstituted heteroalkyl,R₂₆-substituted or unsubstituted heterocycloalkyl, R₂₆-substituted orunsubstituted aryl, or R₂₆-substituted or unsubstituted heteroaryl. R₂₆is independently —NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₂₇-substituted orunsubstituted alkyl, R₂₇-substituted or unsubstituted cycloalkyl,R₂₇-substituted or unsubstituted heteroalkyl, R₂₇-substituted orunsubstituted heterocycloalkyl, R₂₇-substituted or unsubstituted aryl,or R₂₇-substituted or unsubstituted heteroaryl. R₂₇ is independently—NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₂₈-substituted or unsubstituted alkyl,R₂₈-substituted or unsubstituted cycloalkyl, R₂₈-substituted orunsubstituted heteroalkyl, R₂₈-substituted or unsubstitutedheterocycloalkyl, R₂₈-substituted or unsubstituted aryl, orR₂₈-substituted or unsubstituted heteroaryl. R₂₈ is independentlyunsubstituted alkyl, unsubstituted cycloalkyl, unsubstitutedheteroalkyl, unsubstituted heterocycloalkyl, unsubstituted aryl orunsubstituted heteroaryl.

R₃₀ and R₃₁ are each independently selected from hydrogen,R₃₂-substituted or unsubstituted alkyl, R₃₂-substituted or unsubstitutedcycloalkyl, R₃₂-substituted or unsubstituted heteroalkyl,R₃₂-substituted or unsubstituted heterocycloalkyl, R₃₂-substituted orunsubstituted aryl, or R₃₂-substituted or unsubstituted heteroaryl. R₃₂is independently —NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₃₃-substituted orunsubstituted alkyl, R₃₃-substituted or unsubstituted cycloalkyl,R₃₃-substituted or unsubstituted heteroalkyl, R₃₃-substituted orunsubstituted heterocycloalkyl, R₃₃-substituted or unsubstituted aryl,or R₃₃-substituted or unsubstituted heteroaryl. R₃₃ is independently—NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₃₄-substituted or unsubstituted alkyl,R₃₄-substituted or unsubstituted cycloalkyl, R₃₄-substituted orunsubstituted heteroalkyl, R₃₄-substituted or unsubstitutedheterocycloalkyl, R₃₄-substituted or unsubstituted aryl, orR₃₄-substituted or unsubstituted heteroaryl. R₃₄ is independentlyunsubstituted alkyl, unsubstituted cycloalkyl, unsubstitutedheteroalkyl, unsubstituted heterocycloalkyl, unsubstituted aryl orunsubstituted heteroaryl. In some embodiments, R₃₀ and R₃₁ are eachindependently hydrogen or an unsubstituted lower alkyl. In anotherembodiment, R₃₀ and R₃₁ are each hydrogen.

In some embodiments, R₃₀ and R₃₁ together form a single bond (therebycreating a structure of Formula I) or are they are substituents (e.g.,substituted or unsubstituted alkyl or substituted or unsubstitutedheteroalkyl) joined together to form a heteroocyclic ring including Xand Y.

It is understood that each substituent on an alkyl, cycloalkyl,heteroalkyl, heterocycloalkyl, aryl or heteroaryl may occur multipletimes, each occurrence being independently chosen.

It is understood that the position in the heterocycle of Formula I whichis vicinal to X can be an asymmetric center. Accordingly, the (R) and(S) enantiomers of Formula I are contemplated for compounds of describedherein, as shown following.

Any of the Formulae herein may be similarly designated R and S. Unlessspecifically indicated to the contrary, the compounds contemplatedherein include all optical isomers, regioisomers, enantiomers and/ordiastereomers thereof. In one embodiment, the compound is the Renantiomer.

In some embodiments, the compound has the structure of Formula I,provided however that the compound is not lipoic acid.

1. Amides

In some embodiments, the compound is an optionally substitutedheterocyclic amide having the structure of Formula II:

wherein R₁₉, R₂₀, R₂₁, R₃₀, R₃₁, X and Y are as defined above.

In some embodiments, the compound of Formula II has the structure ofFormula III:

where R₂₀ and R₂₁ are as defined above.

In some embodiments, R₂₁ is R₂₆-substituted alkyl or R₂₆-substitutedheteroalkyl, wherein R₂₆ is present in one or more occurrences, and ineach occurrence is independently amine, —NH₂, ═NH, —PO₃H₂, —OH, —CO₂H,R₂₇-substituted or unsubstituted alkyl, R₂₇-substituted or unsubstitutedcycloalkyl, R₂₇-substituted or unsubstituted heteroalkyl,R₂₇-substituted or unsubstituted heterocycloalkyl, R₂₇-substituted orunsubstituted aryl, or R₂₇-substituted or unsubstituted heteroaryl. Insome embodiments, R₂₁ is aminoalkyl, preferably aminoethyl. In someembodiments, R₂₁ is N-substituted aminoalkyl, preferably N-substitutedaminoethyl, wherein the pendant amino functionality is in turnsubstituted with R₂₇ (e.g., (N,N-dialkylamino)-alkyl, preferablydimethylaminoethyl). In some embodiments, R₂₇ is C₁-C₆ alkyl, preferablymethyl. In some embodiments, R₂₁ is phosphonoylalkyl, preferablyphosphonoylethyl. In some embodiments, R₂, is hydroxyalkyl, preferablyhydroxyethyl. In some embodiments, R₂₁ is hydroxyalkyl, preferablyhydroxyethyl, and R₂₀ is unsubstituted alkyl, preferably C₁-C₆ alkyl,more preferably methyl. In some embodiments, R₂₁ is hydroxyethyl, andR₂₀ is methyl. In some embodiments, R₂₁ is alkyl which in turn ismultiply substituted with —OH (e.g., 2,3-dihydroxypropyl), and R₂₀ ishydrogen.

In some embodiments, R₂₁ is R₂₆-substituted or unsubstitutedheterocycloalkyl. Exemplary heterocycloalkyl functionalities include,but are not limited to, morpholino and piperazinyl. In some embodiments,R₂₁ is R₂₆-substituted tetrahydropyranyl, preferably3,4,5,6-tetrahdroxytetrahydro-2H-pyran-2-yl). In some embodiments, R₂₆is multiply substituted with hydroxyl. In some embodiments, R₂₁ isR₂₆-substituted morpholino, wherein R₂₆ is C₁-C₆ alkyl, preferablymethyl.

In some embodiments, R₂₁ is R₂₆-substituted or unsubstituted heteroaryl,preferably (1H-imidazol-2-yl)ethyl.

In some embodiments, R₂₁ is R₂₆-substituted heteroalkyl, wherein theR₂₆-substituted heteroalkyl includes a repeating polymeric unit.Exemplary polymeric units in this context include, but are not limitedto, polyethylene glycol [(—CH₂—CH₂—O—)_(n), wherein n>1], as known inthe art.

In some embodiments, R₂₁ is as defined above, and R₂₀ is C₁-C₆ alkyl,preferably methyl, ethyl or isopropyl, more preferably methyl.

In some embodiments, R₂₁ is R₂₆-substituted alkyl or R₂₆-substitutedheteroalkyl, wherein R₂₆ is present in one or more occurrences, and ineach occurrence is independently unsubstituted alkyl. In someembodiments, R₂₁ is aminoalkyl, preferably aminoethyl, and R₂₆ isindependently present at the pendant nitrogen 0, 1, 2 or even 3 times.

In some embodiments, R₂₀ and R₂₁ are independently hydrogen.

In some embodiments, the compound of Formula III includes an amino acidbound in amide linkage between an alpha nitrogen of the amino acid or aside chain nitrogen of the amino acid, and the acid functionality oflipoic acid, having the structure of either of Formula IVA-IVBfollowing.

Regarding Formulae IVA-B, the term “AA” refers to an amino acid having aside chain nitrogen in amide linkage with the lipoic acid functionality,and R₂₉ is the side chain of an alpha amino acid, preferably a naturallyoccurring amino acid or homolog thereof. The linkage between the sidechain nitrogen of the amino acid “AA” is indicated by the symbol

in Formulae IVA. Exemplary amino acids include, but are not limited to,the naturally occurring amino acids and homologs thereof (e.g.,diaminoproprionic acid, diaminobutyric acid, ornithine, lysine,homolysine), as known in the art. Both D/L (R/S) stereoisomers of theamino acids are contemplated herein. Further exemplary amino acid amidesof lipoic acid having the structure of Formulae IVA-IVB include, but arenot limited to, the compounds set forth below:

TABLE 2 Amino acid amides

In some embodiments, a compound is provided as set forth below:

TABLE 3 Active agent amides

2. Esters

In some embodiments, there is provided an optionally substitutedheterocyclic-containing ester of Formula I having the structure ofFormula V:

wherein R₁₉, R₂₁, R₃₀, R₃₁, X, and Y are as defined above.

In some embodiments of the compound of Formula V or V-NC, R₁₉ isunsubstituted alkylene, preferably C₁-C₆ alkylene, more preferably C₄alkylene. In some embodiments, R₁₉ is C₁-C₈, preferably C₁-C₆, morepreferably C₄ alkylene independently substituted with one or more R₂₂,wherein R₂₂ is as defined herein.

In some embodiments, the compound of Formula V has the structure ofFormula VI following, wherein R₂₁ is substituted or unsubstituted alkyl,substituted or unsubstituted cycloalkyl, substituted or unsubstitutedheteroalkyl, substituted or unsubstituted heterocycloalkyl, substitutedor unsubstituted aryl, or substituted or unsubstituted heteroaryl.

In some embodiments, R₂₁ is alkyl, preferably C₁-C₆ alkyl, morepreferably C₁-C₃ alkyl, most preferably C₁, C₂, or C₃ alkyl, examples ofwhich include, but are not limited to, the compounds set forth below:

TABLE 4 Active Agent Alkyl Esters

In some embodiments, R₂₁ is alkyl, preferably C₁-C₆ alkyl, morepreferably C₃-C₅ alkyl, most preferably C₃, C₄ or C₅ alkyl, which inturn is multiply substituted with —OH. In some embodiments, R₂₁ is alkylsubstituted with 1, 2, 3, 4 or even 5 hydroxyl functionalities. Alldiastereomeric, enantiomeric and regioisomeric forms of compounds ofFormulae V, VI, VI(R), and VI(S) are contemplated herein.

Exemplary compounds according to any of Formulae V, VI, VI(R), and VI(S)include, but are not limited to, the compounds set forth below:

TABLE 5 Active Agent Substituted Alkyl Esters

In some embodiments, R₂₁ is R₂₆-substituted or unsubstituted alkyl orR₂₆-substituted or unsubstituted heteroalkyl, and R₂₆ is independently—NH₂, ═NH, —PO₃H₂, —OH, —CO₂H, R₂₇-substituted or unsubstituted alkyl,R₂₇-substituted or unsubstituted cycloalkyl, R₂₇-substituted orunsubstituted heteroalkyl, R₂₇-substituted or unsubstitutedheterocycloalkyl, R₂₇-substituted or unsubstituted aryl, orR₂₇-substituted or unsubstituted heteroaryl.

In some embodiments, R₂₁ is R₂₆-substituted alkyl or R₂₆-substitutedheteroalkyl, wherein R₂₆ is independently present in one or moreoccurrences, and in each occurrence is independently unsubstitutedalkyl, preferably methyl. In some embodiments, R₂₁ is aminoalkyl,preferably aminoethyl, and R₂₆ is independently present at the pendantnitrogen 0, 1, 2 or even 3 times. In some embodiments, R₂₁ is a cholinesubstituent in ester attachment with the lipoic acid structure set forthbelow. The structure may include a counterion, wherein the counterion isany pharmaceutically acceptable counterion capable of forming a saltwith the choline lipoate:

In some embodiments, a substituted group substituted with at least onesubstituent group. More specifically, in some embodiments, eachsubstituted alkyl, substituted heteroalkyl, substituted cycloalkyl,substituted heterocycloalkyl, substituted aryl, substituted heteroaryl,substituted alkylene, substituted heteroalkylene, substitutedcycloalkylene, substituted heterocycloalkylene, substituted arylene orsubstituted heteroarylene within a compound described herein issubstituted with at least one substituent group. In other embodiments,at least one or all of these groups are substituted with at least onesize-limited substituent group. Alternatively, at least one or all ofthese groups are substituted with at least one lower substituent group.

C. Salts

The compounds described herein can also be provided as apharmaceutically acceptable salt. The term “pharmaceutically acceptablesalt” includes salts of the active compounds that are prepared withrelatively nontoxic acids or bases, depending on the particularsubstituents found on the compounds described herein. When compounds ofthe present invention contain relatively acidic functionalities, baseaddition salts can be obtained by contacting the neutral form of suchcompounds with a sufficient amount of the desired base, either neat orin a suitable inert solvent. Examples of pharmaceutically acceptablebase addition salts include sodium, potassium, calcium, ammonium,organic amino, or magnesium salt, or a similar salt. When compounds ofthe present invention contain relatively basic functionalities, acidaddition salts can be obtained by contacting the neutral form of suchcompounds with a sufficient amount of the desired acid, either neat orin a suitable inert solvent. Examples of pharmaceutically acceptableacid addition salts include those derived from inorganic acids likehydrochloric, hydrobromic, nitric, carbonic, monohydrogencarbonic,phosphoric, monohydrogenphosphoric, dihydrogenphosphoric, sulfuric,monohydrogensulfuric, hydriodic, or phosphorous acids and the like, aswell as the salts derived from relatively nontoxic organic acids likeacetic, propionic, isobutyric, maleic, malonic, benzoic, succinic,suberic, fumaric, lactic, mandelic, phthalic, benzenesulfonic,p-tolylsulfonic, citric, tartaric, oxalic, methanesulfonic, and thelike. Also included are salts of amino acids such as arginate and thelike, and salts of organic acids like glucuronic or galactunoric acidsand the like (see, for example, Berge et al., “Pharmaceutical Salts”,Journal of Pharmaceutical Science, 1977, 66, 1-19). Certain specificcompounds of the present invention contain both basic and acidicfunctionalities that allow the compounds to be converted into eitherbase or acid addition salts.

Thus, the compounds of the present invention may exist as salts, such aswith pharmaceutically acceptable acids. The present invention includessuch salts. Examples of such salts include, but are limited to,hydrochlorides, hydrobromides, sulfates, methanesulfonates, nitrates,maleates, acetates, citrates, fumarates, tartrates (e.g., (+)-tartrates,(−)-tartrates, or mixtures thereof including racemic mixtures),succinates, benzoates, and salts with amino acids such as glutamic acid.These salts may be prepared by methods known to those skilled in theart.

The neutral forms of the compounds are preferably regenerated bycontacting the salt with a base or acid and isolating the parentcompound in the conventional manner. The parent form of the compounddiffers from the various salt forms in certain physical properties, suchas solubility in polar solvents.

In one embodiment, the counterion ion is the1,3-dihydroxy-2-(hydroxymethyl)propan-2-aminium cation (i.e., atromethamine salt):

III. Methods of Use

The agents described herein can be employed in a method including thestep of providing an active agent to a cell, either in vitro or in vivo.

The active agents described herein can be employed in a method fortreating or preventing oxidation damage to cells. Such a method includesthe step of administering a pharmaceutical composition comprising anactive agent to a cell, either in vitro or in vive.

As stated above, the agents can be delivered to cells in vitro or invivo. In one embodiment, the cells are in vivo. In either case, thecells can be ocular cells, e.g., lens cells. In one embodiment, theagent is delivered to a lens, either in vitro or in vivo. Becauseoxidative damage has been implicated in other disorders includingcancer, the agents may prove useful for administration to any type ofcell exhibiting or prone to oxidative damage.

In one embodiment, the compounds described herein can be used in amethod for treating ocular disease. Exemplary ocular diseases include,but are not limited to: presbyopia, cataract, macular degeneration(including age-related macular degeneration), retinopathies (includingdiabetic retinopathy), glaucoma, and ocular inflammations. In oneembodiment, the ocular disease to be treated is cataract. In anotherembodiment, the ocular disease to be treated is treat presbyopia.

The methods preferably utilize a therapeutically effective amount of theactive agent. The term “therapeutically effective amount” means anamount that is capable of preventing, reducing, reversing, and/orslowing the rate of oxidative damage. For ocular applications, atherapeutically effective amount may be determined by measuring clinicaloutcomes including, but not limited to, the elasticity, stiffness,viscosity, density, or opacity of a lens.

Lens elasticity decreases with age and is a primary diagnostic andcausative factor for presbyopia. Lens elasticity can be measured asaccommodative amplitude in diopters (D). FIG. 1 depicts the averageelasticity in diopters of an untreated human lens as a function of agein years. The lower the value of D, the less elastic the lens. In oneembodiment, the agents described herein can decrease and/or maintain Dat a value that is greater than the D value exhibited by an untreatedlens of about the same age. In other words, the agents can keepaccommodative amplitude “above the line” depicted in FIG. 1 (the solidline is mean accommodative amplitude). In one embodiment, D is increasedand/or maintained at a value about 2, 5, 7, 10, 15, 25, 50, 100, 150, or200 percent above the line. However, as individual lenses may differwith respect to average values, another embodiment provides any increasein accommodative amplitude, maintenance of accommodative amplitude, orreduction in the rate of decline of accommodative amplitude (i.e.,reduction in the rate of decrease in diopters) for an individual lenscompared to the accommodative amplitude of the same lens beforetreatment. Accordingly, in another embodiment, the methods provide anincrease in accommodative amplitude of about 0.25 to about 8 diopters,or at least about 0.1, 0.2, 0.25, 0.5, 1, 1.2, 1.5, 1.8, 2, 2.5, 3, 5,or 8 diopters compared to the same lens before treatment.

Lens elasticity can also be measured by the unit of elasticity E. Thehigher the value of E, the less elastic the lens. FIG. 2 depicts theaverage elasticity (E) of an untreated human lens as a function of agein years. In one embodiment, the agents described herein can decreaseand/or maintain E at a value that is less than the E value exhibited byan untreated lens of about the same age. In other words, the agents cankeep lens elasticity “below the line” depicted in FIG. 2. In oneembodiment, E is decreased and/or maintained at a value about 2, 5, 7,10, 15, 25, 50, 100, 150, or 200 percent below the line. However, asindividual lenses may differ with respect to average values, anotherembodiment provides any increase in elasticity, maintenance ofelasticity, or reduction in the rate of decline of elasticity (i.e.,reduction in the rate of increase in E value) for an individual lenscompared to the elasticity of the same lens before treatment.

Therapeutic efficacy can also be measured in terms of lens opacity. Lensopacity increases with age and is a primary diagnostic and causativefactor for cataract. FIG. 3 depicts the average opacity of an untreatedhuman lens as a function of age in years. In one embodiment, the agentsdescribed herein can decrease and/or maintain opacity at a value that isless than the opacity value exhibited by an untreated lens of about thesame age. In other words, the agents can keep lens opacity “below theline” depicted in FIG. 3. In one embodiment, lens elasticity isdecreased and/or maintained at a value about 2, 5, 7, 10, 15, 25, 50,100, 150, or 200 percent below the line. However, as individual lensesmay differ with respect to average values, another embodiment providesany decrease, maintenance, or reduction in the rate of increase ofopacity for an individual lens compared to the opacity of the same lensbefore treatment.

Therapeutic efficacy can also be measured as a reduction in the rate ofcell proliferation, particularly lens epithelial cell proliferation.Thus, in some embodiments, therapeutic efficacy can be measured bycytostatic effect.

The active agent can be administered as a racemate or as an enantiomer.For example, lipoic acid and its derivatives are preferably administeredto include the R form; cystine and its derivatives are preferablyadministered to include the L form. Synthetic methods to yield aracemate may be less expensive than stereo-specific processes includingisolation/purification steps. On the other hand, administering a singleenantiomer can lower the therapeutically effective amount, thusdecreasing toxicity effects.

The agents described herein are preferably reducing agents. For example,the agents can possess a redox potential E₀′ (V) of about −0.01 to about−1.0, about −0.1 to about −0.5, about −0.2 to about −0.4, or about −0.3.The agents described herein preferably exhibit an acceptable toxicityprofile, e.g., a median lethal dose (LD₅₀) of at least 10 μM, at least20 μM, at least 40 μM, or at least 1 mM. Toxicity can be assessed by anymethod known in the art such as, for example, viability of humanumbilical vein endothelial cells (HUVEC, first passage) using theMultiTox-Fluor assay (Promega) or Live/Dead® assay (Invitrogen). Ofcourse, agents selected as pharmaceutical agents for the treatment ofpresbyopia should exhibit both antioxidant efficacy (reducing power) aswell as a desirable safety profile (low toxicity). Accordingly, in oneembodiment, a screening method is provided whereby dithiol compounds orderivatives are tested for reducing power and/or toxicity. In anotherembodiment, a method includes screening dithiol compounds or dithiolderivatives for their ability to increase lens elasticity either invitro or in vivo.

The agents described herein preferably exhibit favorable membranepermeability, specifically corneal permeability. Corneal penetration canbe measured by methods known in the art, such as, for example, thosedisclosed in Kim et al. (2005) “Aqueous penetration and biologicalactivity of moxifloxacin 0.5% ophthalmic solution and gatifloxacin 0.3%solution in cataract surgery patients” Ophthalmology 112(11):1992-96. Inone embodiment, the agent enters the lens epithelial cells using anaturally occurring transport mechanism. For example, lipoic acid andcystine enter lens cells via specific plasma membrane symporters andantiporters. By using lipoic acid, cystine, or derivatives thereof, onecan utilize a naturally occurring transport mechanism to deliver theagents to the lens cells.

Some agents described herein exist naturally in the untreated eye.Lipoic acid and cystine, for example, occur naturally in eye tissue. Ingeneral, a therapeutically effective amount of the exogenouslyadministered agent is often at least about 1 or 2 orders of magnitudelarger than the natural level of the agent. In one embodiment, thelipoic acid or derivative thereof is administered in a dose amount of upto about 1 mM. In one embodiment, the dose amount of lipoic acid or aderivative thereof is about 1 μM up to 1 mM, preferably about 0.25 mM toabout 0.75 mM, or about 0.5 mM. In another embodiment, the dose amountof lipoic acid or derivative thereof is no more than 0.5 mM, 250 μM, 100μM, 50 μM, 20 μM, or 10 μM. In another embodiment, cystine or aderivative thereof is administered in a dose amount of about 1 μM toabout 20 μM. In yet another embodiment, the dose amount of cystine or aderivative thereof is no more than 20 μM, the limit of cystinesolubility in aqueous solution, or no more than 15 μM, 12 μM, 10 μM, 7μM, or 5 μM. The dose amount will depend on the route of administrationas well as the age and condition of the patient. Similarly, thefrequency of dosing will depend on similar factors as can be determinedby one of ordinary skill in the art.

Efficacy has been demonstrated in vitro for specific exemplary dosing.FIG. 2 shows that the inelasticity increases by a factor of nearly 20during the critical period from age 40 to 55 years. From current data, a10 μM dose can decrease the inelasticity over 95% within a millimetervolume element (voxel). Extrapolation of these results to a volumeelement in the human lens suggests that using this treatment dose on a55 year old person with a 10 kPA lens starting modulus value (see FIG.2) could be reduced after treatment to a value of about 0.5 kPA (whichthen corresponds to a value typically seen with a 40 yr old person).FIG. 1 permits a conversion of these modulus values to opticalamplitude: accommodative amplitude is normally reduced to almost 0 above55 years, while a person at 40-45 years still exhibits around 4-5diopters of accommodation.

The methods include preventative methods that can be performed onpatients of any age. The methods also include therapeutic methods thatcan be performed on patients of any age, particularly patients that areat least 20, 25, 30, 35, 40, 45, 50, 52, 55, 57, 60, 70, 75, or 80 yearsof age.

IV. Pharmaceutical Compositions

In another embodiment, a pharmaceutical composition includes an agent asdescribed herein and a pharmaceutically acceptable carrier. A“pharmaceutically acceptable carrier,” as used herein refers topharmaceutical excipients, for example, pharmaceutically,physiologically, acceptable organic or inorganic carrier substancessuitable for enteral or parenteral application that do not deleteriouslyreact with the active agent. Suitable pharmaceutically acceptablecarriers include water, salt solutions (such as Ringer's solution),alcohols, oils, gelatins, and carbohydrates such as lactose, amylose orstarch, fatty acid esters, hydroxymethyl cellulose, and polyvinylpyrrolidine. Such preparations can be sterilized and, if desired, mixedwith auxiliary agents such as lubricants, preservatives, stabilizers,wetting agents, emulsifiers, salts for influencing osmotic pressure,buffers, coloring, and/or aromatic substances and the like that do notdeleteriously react with the compounds of the invention.

The pharmaceutical composition may also contain one or more excipientsas is well known in the art of pharmaceutical formulary. In oneembodiment, the pharmaceutical composition is formulated for ocular use.That is, the pharmaceutically acceptable carrier and/or other excipientsare selected to be compatible with, and suitable for, ocular use. Suchcarriers and excipients are well known in the art. The excipients mayalso be selected and/or formulated to improve the solubility of thecompound. For example, the pharmaceutical composition can include one ormore of emulsifiers, buffers, salts, preservatives, lubricants,polymers, solvents, and other known excipients for ocular pharmaceuticalformulations. In one embodiment, the pharmaceutical composition includesan emulsifier and a buffered carrier such as Polysorbate 80 in HBSS(Hank's Balanced Salt Solution).

In one aspect, there is provided a pharmaceutical composition whichincludes a compound or pharmaceutically acceptable salt thereof incombination (e.g., in formulation) with a pharmaceutically acceptableexcipient.

The compounds described herein can be formulated to achieve any deliverysystem known in the art such as immediate or sustained release delivery;systemic, ocular, or localized delivery; topical or injection delivery;prodrug or caged delivery systems, e.g., coumarin cages (as described,for example, in co-pending application U.S. Ser. No. 12/267,260), andthe like.

Liquid form preparations include solutions, suspensions, and emulsions,for example, water or water/propylene glycol solutions. Aqueoussolutions suitable for oral use can be prepared by dissolving the activecomponent in water and adding suitable colorants, flavors, stabilizers,and thickening agents as desired. Aqueous suspensions suitable for oraluse can be made by dispersing the finely divided active component inwater with viscous material, such as natural or synthetic gums, resins,methylcellulose, sodium carboxymethyl cellulose, and other well-knownsuspending agents. Also included are solid form preparations that areintended to be converted, shortly before use, to liquid formpreparations for oral administration. Such liquid forms includesolutions, suspensions, and emulsions. These preparations may contain,in addition to the active component, colorants, flavors, stabilizers,buffers, artificial and natural sweeteners, dispersants, thickeners,solubilizing agents, and the like.

Some compounds may have limited solubility in water and therefore mayrequire a surfactant or other appropriate co-solvent in the composition.Such co-solvents include: Polysorbate 20, 60, and 80; Pluronic F-68,F-84, and P-103; cyclodextrin; and polyoxyl 35 castor oil. Suchco-solvents are typically employed at a level between about 0.01% andabout 2% by weight.

Viscosity greater than that of simple aqueous solutions may be desirableto decrease variability in dispensing the formulations, to decreasephysical separation of components of a suspension or emulsion offormulation, and/or otherwise to improve the formulation. Such viscositybuilding agents include, for example, polyvinyl alcohol, polyvinylpyrrolidone, methyl cellulose, hydroxy propyl methylcellulose,hydroxyethyl cellulose, carboxymethyl cellulose, hydroxy propylcellulose, chondroitin sulfate and salts thereof, hyaluronic acid andsalts thereof, and combinations of the foregoing. Such agents aretypically employed at a level between about 0.01% and about 2% byweight.

The compositions of the present invention may additionally includecomponents to provide sustained release and/or comfort. Such componentsinclude high molecular weight, anionic mucomimetic polymers, gellingpolysaccharides, and finely-divided drug carrier substrates, as known inthe art.

The compounds can be administered to a lens by any route ofadministration including, but not limited to, topical, subtenons,subconjunctival, intracameral, intravitreal, or iontophoresis routes. Inone embodiment, the agent can be delivered topically, e.g., via an eyedrop, gel, ointment, or salve. In other embodiment, the compound can bedelivered via an acute delivery system, e.g., using nanotubes, localinjection, micro-injection, syringe or scleral deposition, orultrasound.

Pharmaceutical compositions provided by the present invention includecompositions wherein the active ingredient is contained in atherapeutically effective amount, i.e., in an amount effective toachieve its intended purpose. The actual amount effective for aparticular application will depend, inter alia, on the condition beingtreated. For example, when administered in methods to treat cancer, suchcompositions will contain an amount of active ingredient effective toachieve the desired result (e.g. decreasing the number of cancer cellsin a subject).

A. Dose Amounts

In one embodiment, the active agent is present in the pharmaceuticalcomposition in an amount of about 0.1% to about 10% by weight, morespecifically about 0.25% to about 10%, about 0.5% to about 10%, about 1%to about 8%, about 3% to about 7%, about 2% to about 5%, about 5% toabout 7%, or about 5%. In another embodiment, the active agent ispresent in the pharmaceutical composition in an amount about 1 μM up to1 mM, preferably about 0.25 mM to about 0.75 mM, or about 0.5 mM.

In some embodiments, a relatively low dose is called for. One suchcircumstance may be a preventative composition where the objective is toprevent rather than reverse oxidative damage. Another circumstance maybe a priming or starting dose that would be titrated upward according tothe subject's responsiveness and treatment objectives. In someembodiment, the active agent is present in an amount of about 0.1% toabout 5%, about 0.1% to about 3%, about 0.1% to about 1%, about 1% toabout 3%. In some embodiments, the active agent is present in an amountof less than about 250 μM, about 5 μM to about 250 M, or about 10 μM toabout 100 μM.

The dosage and frequency (single or multiple doses) of compoundadministered can vary depending upon a variety of factors, includingroute of administration; size, age, sex, health, body weight, body massindex, and diet of the recipient; nature and extent of symptoms of thedisease being treated; presence of other diseases or otherhealth-related problems; kind of concurrent treatment; and complicationsfrom any disease or treatment regimen. Other therapeutic regimens oragents can be used in conjunction with the methods and compounds of theinvention.

Therapeutically effective amounts for use in humans may be determinedfrom animal models. For example, a dose for humans can be formulated toachieve a concentration that has been found to be effective in animals.The dosage in humans can be adjusted by monitoring presbyopia in thehuman subject and adjusting the dosage upwards or downwards, asdescribed above.

Dosages may be varied depending upon the requirements of the subject andthe compound being employed. The dose administered to a subject, in thecontext of the present invention, should be sufficient to effect abeneficial therapeutic response in the subject over time. The size ofthe dose also will be determined by the existence, nature, and extent ofany adverse side effects. Generally, treatment is initiated with smallerdosages, which are less than the optimum dose of the compound.Thereafter, the dosage is increased by small increments until theoptimum effect under circumstances is reached. Dosage amounts andintervals can be adjusted individually to provide levels of theadministered compound effective for the particular clinical indicationbeing treated. This will provide a therapeutic regimen that iscommensurate with the severity of the disease state of the subject.

The ratio between toxicity and therapeutic effect for a particularcompound is its therapeutic index and can be expressed as the ratiobetween LD₅₀ (the amount of compound lethal in 50% of the population)ED₅₀ (the amount of compound effective in 50% of the population).Compounds that exhibit high therapeutic indices are preferred.Therapeutic index data obtained from cell culture assays and/or animalstudies can be used in formulating a range of dosages for use in humans.The dosage of such compounds preferably lies within a range of plasmaconcentrations that include the ED₅₀ with little or no toxicity. Thedosage may vary within this range depending upon the dosage formemployed and the route of administration utilized. See, e.g. Fingl etal., In: THE PHARMACOLOGICAL BASIS OF THERAPEUTICS, Ch. 1, p. 1, 1975.The exact formulation, route of administration, and dosage can be chosenby the individual physician in view of the patient's condition and theparticular method in which the compound is used.

B. Co-Administration of Additional Active Agents

The compounds described herein can be used in combination with oneanother, with other active agents known to be useful in ocular disease,or with adjunctive agents that may not be effective alone, but maycontribute to the efficacy of the active agent. For example, adjunctiveagents might include one or more amino acids or choline to enhance theefficacy of the active agent. The combinations can be advantageous,e.g., in reducing metabolic degradation.

The term “co-administer” means to administer more than one active agent,such that the duration of physiological effect of one active agentoverlaps with the physiological effect of a second active agent. In someembodiments, co-administration includes administering one active agentwithin 0.5, 1, 2, 4, 6, 8, 10, 12, 16, 20, or 24 hours of a secondactive agent. Co-administration includes administering two active agentssimultaneously, approximately simultaneously (e.g., within about 1, 5,10, 15, 20, or 30 minutes of each other), or sequentially in any order.In some embodiments, co-administration can be accomplished byco-formulation, i.e., preparing a single pharmaceutical compositionincluding both active agents. In other embodiments, the active agentscan be formulated separately. In another embodiment, the active and/oradjunctive agents may be linked or conjugated to one another.

Without being bound by theory, it is believed that the administration ofan active agent, e.g., lipoic acid or a derivative thereof, and anadjunctive agent such as choline, can be particularly advantageous in aconjugated form. The conjugate compound be applied to the cornea, andpenetration is achieved due to the bi-phasic (water and lipid soluble)nature of the conjugate compound. As the conjugate goes through thecornea, naturally present esterases (enzymes) separate lipoic acid fromcholine. The lipoic acid (now a pro-drug) in the aqueous bathes the lensand enters the lens epithelial cells (due to low molecular weight andsize), and there is reduced by any one of several oxido-reductases(enzymes such as thioredoxin and thioltransferase) to form dihydrolipoicacid. Dihydrolipoic acid now has two extra hydrogen atoms to donate to adisulfide complex (e.g., protein disulfide PSSP), separating the twosulfur atoms into sulfhydril molecules (e.g., protein cysteine residuesPSH with free SH groups) thus breaking the inter-cytosol proteincross-links. Breaking these cross-link is what reduces the lensstiffness. Once donation of the hydrogen atoms to the sulfur atom, thedihydrolipoic acid becomes lipoic acid and is available for recycling inthe cell to become dihydrolipoic acid or converted to a natural degradedby product thiolactone and excreted.

C. Co-Administration with a Biochemical Energy Source

In one embodiment, a reducing agent, such as one of the compoundsdescribed herein, is co-administered with a biochemical energy source. Abiochemical energy source facilitates reduction by participating as anintermediate of energy metabolic pathways, particularly the glucosemetabolic pathway. Exemplary intermediates of this pathway are depictedby, e.g., Zwingmann, C. et al. 2001. 13C Isotopomer Analysis of Glucoseand Alanine Metabolism Reveals Cytosolic Pyruvate Compartmentation asPart of Energy Metabolism in Astrocytes. GLIA 34:200-212. Exemplarybiochemical energy sources include, e.g., glucose or a portion thereof(e.g., glucose-6-phosphate (G6P)), pyruvate (e.g., ethyl pyruvate),NADPH, lactate or derivative thereof. G6P may be favored over glucosesince a formulation including glucose may further benefit from theaddition of preservatives. In one embodiment, the biochemical energysource is an intermediate in a cytosolic metabolic pathway. Exemplarycytosolic pathway intermediates include, e.g., glucose, pyruvate,lactate, alanine, glutamate, and 2-oxoglutarate. In another embodiment,the biochemical energy source is an intermediate in a mitochondrialmetabolic pathway. Exemplary mitochondrial pathway intermediatesinclude, e.g., pyruvate, TCA-cycle intermediates, 2-oxoglutarate,glutamate, and glutamine. In one embodiment, the biochemical energysource is pyruvate compound (e.g., ethyl pyruvate). In anotherembodiment, the biochemical energy source is alanine.

In one embodiment, the agent is co-administered with glucose-6-phosphate(G6P), NADPH, or glucose. In one embodiment, the agent is activated byan endogenous chemical energy, e.g., endogenous glucose. For example,endogenous glucose can activate lipoic acid or a derivative thereof todihydrolipoic acid (DHLA) or a corresponding derivative thereof.

EXAMPLES Example 1 In Vitro Efficacy Studies

Increase in Elasticity: Pairs of mouse lenses were incubated in medium200 supplemented with an antibiotic, an antimycotic, in the presence orabsence of lipoic acid (concentrations ranging from 0.5 μM to 500 μM)for 8-15 hours. Each lens was removed from medium, weighed, andphotographed on a micrometer scale. A coverslip of known weight(0.17899±0.00200 g) was placed on the lens, and the lens wasphotographed again on the micrometer scale. The diameter of each lenswith and without the coverslip was determined from the photographs. Thechange in lens diameter produced by the force (coverslip) was computedΔD=(D_(withcoverslip)−D_(withoutcoverslip)). The results (FIG. 4, $)indicate that lipoic acid at concentrations ≧9.6 μM caused astatistically significant increase in ΔD, p<0.0001.

Decrease in disulfide bonds: Lipoic acid at concentrations ≧9.6 μMcaused a statistically significant decrease in protein disulfides in themouse lenses where there was a significant increase in ΔD (FIG. 4).Mouse lenses were homogenized in a denaturing buffer containing afluorescent alkylating agent to modify the free SH groups. Afterremoving the alkylating agent homogenates were reduced and alkylatedwith a different fluorescent alkylating agent. Absorption spectra of themodified proteins were used to calculate free protein SH and protein SSgroups. The results are shown in FIG. 5.

Example 2 Synthesis of (R)-Lipoamide

NHS ester of (R)-lipoic acid. The NHS ester of (R)-lipoic acid wassynthesized as described in Scheme 1 following.

A solution of lipoic acid (25.6 g, 124 mmol), N-hydroxysuccinimide (15.6g, 136 mmol), and EDC (26.1 g, 136 mmol) in anhydrous CH₂Cl₂ (300 mL)was stirred overnight at room temperature. The reaction mixture wasdiluted with ethyl acetate (500 mL) and washed with H2O (500 mL),saturated aqueous NaHCO₃ (500 mL), saturated aqueous NaCl (500 mL) anddried (MgSO₄). The drying agent was removed by filtration and thefiltrate was concentrated to dryness giving the product as a yellow sold(35.4 g, 94%).

(R)-Lipoamide. (R)-lipoamide was synthesized as described in Scheme 2following.

A solution of the NHS ester (2.7 g, 8.9 mmol) in anhydrous CH₂Cl₂ (50mL) was cooled in a dry ice acetone bath. Ammonia was condensed into thereaction mixture over a period of 1-2 hours, then the reaction mixturewas allowed to warm to room temperature overnight and diluted withCH₂Cl₂ (50 mL). Water (100 mL) was added and the mixture was stirred for20 minutes. The phases were separated. The organic phase was washed withsaturated aqueous NaCl (100 mL) and dried (Na₂SO₄). The drying agent wasremoved by filtration and the filtrate was concentrated to drynessgiving the product as a yellow microcrystalline sold (1.56 g, 85%).

Example 3 Synthesis of an Arginine-Lipoic Acid Conjugate (“LA-Arg”)

Pentafluorophenyl ester of (R)-lipoic acid. The pentafluorophenyl esterof (R)-lipoic acid was synthesis as described in Scheme 3 following.

Solid EDC (1.04 g, 5.4 mmol) was added at once to a solution of lipoicacid (1.0 g, 4.8 mmol), and pentafluorophenol (1 g, 5.4 mmol) inanhydrous CH₂Cl₂:DMF (14 mL; (6:1)). The solution was stirred overnightat room temperature then concentrated to dryness. Flash columnchromatography (SiO₂, 100% DCM) afforded the product as a clear, thickyellow oil (1.67 g, 94%).

LA-Arg. The arginine-lipoic acid conjugate was synthesis as described inScheme 4 following.

L-Arginine (530 mg, 3.1 mmol) was added at once to a solution of the Pfpester (1.34 g, 3.6 mmol) in anhydrous DMF (4 mL). The reaction mixturewas stirred at room temperature for 48 hours. Insolubles were isolatedby vacuum filtration and the filter cake was washed with CHCl₃ (20 mL).The material was dried in vacuo overnight giving the product as a paleyellow solid (340 mg, 26%).

Example 4 Syntheses of Lipoic Acid Choline Ester

Lipoic acid choline ester was prepared according to the followingsynthetic route. Choline salts of alternative reducing agents can besimilarly prepared by making the appropriate reagents substitutions.Also, one of ordinary skill in the art would recognize that thesesyntheses are provided as guidance and that reagents, conditions,amounts, temperatures, and the like may be modified without departingfrom the general synthetic pathway.

Step 1

(R)-2-(dimethylamino)ethyl 5-(1,2-dithiolan-3-yl)pentanoate. A solutionof DCC (11 g, 53 mmol) in anhydrous CH₂Cl₂ (20 mL) was added withstirring over 10-20 minutes to a cold (0° C.) solution of R-lipoic acid(10.0 g, 48.5 mmol), N,N-dimethylethanolamine (14.5 mL, 145 mmol, 3eq.), and DMAP (600 mg, 4.9 mmol) in anhydrous CH₂Cl₂ (50 mL). Followingcomplete addition, the cold bath was removed. After 18 hours at roomtemperature, all volatiles were removed under reduced pressure, and theresulting residue was purified by flash column chromatography (SiO₂, 2%MeOH in CH₂Cl₂) providing the desired product as a clear yellow oil(10.6 g, 79%). All data consistent with values reported in theliterature. (See Courvoisier C. et al. 2006. Synthesis and effects of3-methylthiopropanoyl thiolesters of lipoic acid, methional metabolitemimics. Bioorganic Chemistry 34(1):49-58.)

Step 2

(R)-2-(5-(1,2-dithiolan-3-yl)pentanoyloxy)-N,N,N-(trimethyl)ethylammoniumiodide. Methyl iodide (0.55 mL, 9.0 mmol) was added to a solution of theamine (2.5 g, 9.0 mmol) in anhydrous CH₂Cl₂ (20 mL). The reactionmixture was stirred overnight and slowly poured into diethyl ether (250mL) with vigorous stirring. The choline salt was isolated by filtrationas a free-flowing pale, yellow sold (3.7 g, 98%).

Example 4b One-Step Synthetic Route

Example 5 Eye Drop Formulation of Lipoic Acid Choline Ester

The following eye drop formulation was prepared using lipoic acidcholine ester as the active agent.

Formula A

Concentration Ingredient % by weight Purpose Lipoic acid choline ester5.0 Active agent Ethyl pyruvate 0.1 Energy source Sodium phosphate 0.269Buffer monobasic monohydrate, USP Sodium phosphate 0.433 Buffer dibasicanhydrous, USP Sodium chloride 0.5 Tonicity agentHydroxypropylmethylcellulose 0.2 Viscosity agent (HPMC), USP De-ionized,pyrogen free water to 100 mL SolventFormula B

Concentration Ingredient % by weight Purpose Lipoic acid choline ester5.0 Active agent Alanine 0.5 Stabilizer Sodium phosphate 0.269 Buffermonobasic monohydrate, USP Sodium phosphate 0.433 Buffer dibasicanhydrous, USP Sodium chloride 0.5 Tonicity agentHydroxypropylmethylcellulose 0.2 Viscosity agent (HPMC), USP De-ionized,pyrogen free water to 100 mL Solvent

The eye drop formulation has a pH of 7.0.

The pharmaceutical formulation may be diluted to 100 ml filtered water(e.g., Millex syringe filter (0.45 micron 33 mm). The pharmaceuticalcomposition may be packaged for multi-dose administration, e.g., 2-7 mL(e.g., 5 mL) eyedropper bottle with screw lid dropper.

The examples given above are merely illustrative and are not meant to bean exhaustive list of all possible embodiments, applications, ormodifications of the invention. Thus, various modifications andvariations of the described methods and systems of the invention will beapparent to those skilled in the art without departing from the scopeand spirit of the invention. Although the invention has been describedin connection with specific embodiments, it should be understood thatthe invention as claimed should not be unduly limited to such specificembodiments. Indeed, various modifications of the described modes ofcarrying out the invention which are obvious to those skilled in thechemical arts or in the relevant fields are intended to be within thescope of the appended claims.

The disclosures of all references and publications cited above areexpressly incorporated by reference in their entireties to the sameextent as if each were incorporated by reference individually.

What is claimed is:
 1. A compound having the structure of Formula I orI-NC, or a pharmaceutically acceptable salt thereof:

wherein at least one of X and Y is sulfur, and the other is sulfur,selenium, or a sulfonic group; R₁₉ is substituted or unsubstitutedalkylene; R₂₀, R₂₁, R₃₀, and R₃₁ are each independently hydrogen,substituted or unsubstituted alkyl, substituted or unsubstitutedcycloalkyl, substituted or unsubstituted heteroalkyl, substituted orunsubstituted heterocycloalkyl, substituted or unsubstituted aryl, orsubstituted or unsubstituted heteroaryl; wherein R₃₀ and R₃₁ mayoptionally be joined together or together form a single bond; Z is N andm is
 1. 2. The compound of claim 1, wherein one of X and Y is sulfur,and the other is sulfur or selenium.
 3. The compound of claim 1, whereinX and Y are both sulfur.
 4. The compound of claim 1, wherein R₁₉ isunsubstituted alkylene.
 5. The compound of claim 4, wherein R₁₉ is C₄alkylene.
 6. The compound of claim 5, wherein the compound has astructure of Formula III(R):


7. The compound of claim 6, wherein the compound is:


8. A compound having a structure of Formula IVB, or a pharmaceuticallyacceptable salt thereof:

wherein R₂₉ is the side chain of an alpha amino acid.
 9. The compound ofclaim 8, wherein the compound is:


10. A compound having a structure of Formula VI(R), or apharmaceutically acceptable salt thereof:

wherein R₂₁ is substituted or unsubstituted alkyl, substituted orunsubstituted cycloalkyl, substituted or unsubstituted heteroalkyl,substituted or unsubstituted heterocycloalkyl, substituted orunsubstituted aryl, or substituted or unsubstituted heteroaryl.
 11. Thecompound of claim 10, wherein R₂₁ is alkyl.
 12. The compound of claim11, wherein said compound has the structure


13. The compound of claim 10, wherein the compound is: